Light emitting diode having N-face GaN with roughened surface

ABSTRACT

An LED includes a substrate, a first n-type GaN layer, a connecting layer, a second n-type GaN layer, a light emitting layer, and a p-type GaN layer. The first n-type GaN layer, the connecting layer, and the second n-type GaN layer are formed on the substrate in sequence. The connecting layer is etchable by alkaline solution, and a bottom surface of the second n-type GaN layer facing towards the connecting layer has a roughed exposed portion. The GaN on the bottom surface of the second n-type GaN layer is N-face GaN. A top surface of the second n-type GaN layer facing away from the connecting layer includes a first area and a second area. The light emitting layer and the p-type GaN layer are formed on the first area of the top surface of the second n-type GaN layer in sequence.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is a divisional application of patentapplication Ser. No. 13/233,194, filed on Sep. 15, 2011, entitled“METHOD FOR MANUFACTURING LIGHT EMITTING DIODE BY ETCHING WITH ALKALINESOLUTION”, assigned to the same assignee, and claiming foreign priorityof China patent application No. 201110051041.X filed on Mar. 3, 2011.Thedisclosures of the copending U.S. patent application and the Chinapatent application are incorporated herein by reference in theirentireties.

BACKGROUND

1. Technical Field

The present disclosure relates to semiconductor devices and,particularly, to a light emitting diode and a method for manufacturingthe light emitting diode.

2. Description of Related Art

Light emitting diodes (LEDs) have many beneficial characteristics,including low electrical power consumption, low heat generation, longlifetime, small volume, good impact resistance, fast response andexcellent stability. These characteristics have enabled the LEDs to beused as a light source in electrical appliances and electronic devices.

In general, the light output of an LED depends on the quantum efficiencyof the active layer and the light extraction efficiency. As the lightextraction efficiency increases, the light output of the LED isenhanced. In order to improve the light extraction efficiency, effortsare made to overcome the significant photon loss resulting from totalreflection inside the LED after emission from the active layer.

There are several methods for increasing the light extraction efficiencyof the LED. A typical method for increasing the light extractionefficiency of the LED is to roughen the surface of the LED by etchingthe surface of the LED. However, it is difficult to roughen the surfaceof the conventional LED, and the etching process usually requiresseveral hours; as a result, the efficiency of manufacturing the LED isdecreased.

What is needed is an LED and a method for manufacturing the LED whichcan ameliorate the problem of the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the disclosure can be better understood with referenceto the following drawings. The components in the drawings are notnecessarily drawn to scale, the emphasis instead being placed uponclearly illustrating the principles of the disclosure. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1 is a top plan view of an LED according to an exemplaryembodiment.

FIG. 2 is a cross sectional view of the LED taken along line II-II ofFIG. 1.

FIG. 3 is a photo of an N-face GaN etched by alkaline solution.

FIGS. 4-9 are views showing different steps of a process of a firstmethod for manufacturing the LED of FIG. 2.

FIG. 10 shows steps of a process of a second method of manufacturing theLED of FIG. 2.

DETAILED DESCRIPTION

Embodiments of the present disclosure will now be described in detailbelow, with reference to the accompanying drawing.

Referring to FIG. 1 and FIG. 2, an LED 100 according to an exemplaryembodiment is shown. The LED 100 includes a substrate 10, a first n-typeGaN layer 20, a connecting layer 30, a second n-type GaN layer 40, alight emitting layer 50, a p-type GaN layer 60, a transparent conductivelayer 70, a p-type electrode 80, and an n-type electrode 90.

The substrate 10 can be made of a material selected from a groupconsisting of Si, SiC, and sapphire, etc. In the present embodiment, thesubstrate 10 is made of sapphire.

The first n-type GaN layer 20 is formed on the substrate 10. In order toimprove the quality of the first n-type GaN layer 20, a buffer layer 11can be formed on the substrate 10 before forming the first n-type GaNlayer 20. The first n-type GaN layer 20 has a first surface 21 facingaway from the substrate 10. The GaN on the first surface 21 of the firstn-type GaN layer 20 is Ga-face GaN. The Ga-face GaN has lattices thereofwith Ga atoms on surfaces of the lattices. N-face GaN has latticesthereof with N atoms on surfaces of the lattices. The N-face GaN can beetched by alkaline solution under 100 degree centigrade to form aroughened surface with hexagonal pyramid structures (see FIG. 3), butthe Ga-face GaN nearly does not react with alkaline solution under 100degree centigrade.

The connecting layer 30 and the second n-type GaN layer 40 are formed onthe first surface 21 of the first n-type GaN layer 20 in sequence. Theconnecting layer 30 can be etched easily by alkaline solution under 100degrees centigrade. The area of the connecting layer 30 is smaller thanthat of the second n-type GaN layer 40; thus, a bottom surface of thesecond n-type GaN layer 40 facing towards the connecting layer 30 has anexposed portion. The connecting layer 30 can be made of a materialselected from a group consisting of AlN, SiO₂, and silicon nitride. Inthe present embodiment, the connecting layer 30 is made of AlN.Preferably, a thickness of the connecting layer 30 is in a range from 5nm to 1000 nm.

The GaN on the bottom surface of the second n-type GaN layer 40 is theN-face GaN. The exposed portion of the bottom surface of the secondn-type GaN layer 40 is roughed to improve the light extractionefficiency of the LED 100. The second n-type GaN layer 40 has a topsurface facing away from the connecting layer 30, wherein the topsurface includes a first area 41 and a second area 42. The lightemitting layer 50, the p-type GaN layer 60, the transparent conductivelayer 70, and the p-type electrode 80 are formed on the first area 41 insequence. The n-type electrode 90 is formed on the second area 42.

The transparent conductive layer 70 can be made of Ni—Au alloy or indiumtin oxide (ITO). In the present embodiment, the transparent conductivelayer 70 is made of ITO.

In the present embodiment, the p-type electrode 80 includes a roundelectrically connecting portion 81 and a linear electrically spreadingportion 82. The electrically connecting portion 81 and the n-typeelectrode 90 are located at two opposite ends of the LED 100respectively. The electrically spreading portion 82 extends from theelectrically connecting portion 81 towards the n-type electrode 90.

Referring to FIG. 4 to FIG. 9, a first method for manufacturing the LED100 according to the exemplary embodiment is shown. The first methodincludes following steps.

Referring to FIG. 4, the first step is to provide the substrate 10. Thesubstrate 10 can be made of a material selected from a group consistingof Si, SiC, and sapphire, etc.

Referring to FIG. 5, the second step is to form the first n-type GaNlayer 20, the connecting layer 30, the second n-type GaN layer 40, thelight emitting layer 50, the p-type GaN layer 60, and the transparentconductive layer 70 on the substrate 10 in sequence. The first n-typeGaN layer 20, the connecting layer 30, the second n-type GaN layer 40,the light emitting layer 50, the p-type GaN layer 60, and thetransparent conductive layer 70 cooperatively form a semiconductor layer101. In order to improve the quality of the first n-type GaN layer 20, abuffer layer 11 can be formed on the substrate 10 before forming thefirst n-type GaN layer 20. The GaN on the first surface 21 of the firstn-type GaN layer 20 is Ga-face GaN, so that the first n-type GaN layer20 would not be etched by alkaline solution. The connecting layer 30 canbe etched easily by alkaline solution under 100 degree centigrade. Thethickness of the connecting layer 30 is in a range from 5 nm to 1000 nm.The GaN on the bottom surface of the second n-type GaN layer 40 isN-face GaN which can be etched easily by alkaline solution.

Referring to FIG. 6, the third step is to form a number of cuttingchannels 102 on the semiconductor layer 101 to divide the semiconductorlayer 101 into a number of light emitting units 103, and to etch eachlight emitting unit 103 to expose a portion of the second n-type GaNlayer 40 of each light emitting unit 103. The cutting channel 102 runsthrough the transparent conductive layer 70, the p-type GaN layer 60,the light emitting layer 50, the second n-type GaN layer 40, theconnecting layer 30 to expose a portion of the first n-type GaN layer20. It is understood, in other embodiments, the cutting channel 102 cannot run through the connecting layer 30, but only expose the connectinglayer 30. The cutting channels 102 can be formed using inductivelycoupled plasma technology.

Referring to FIG. 7, the fourth step is to form the p-type electrode 80on the transparent conductive layer 70 of each light emitting unit 103,and to form the n-type electrode 90 on the exposed portion of the secondn-type GaN layer 40 of each light emitting unit 103.

Referring to FIG. 8, the fifth step is to use alkaline solution to etchaway opposite lateral ends of the connecting layer 30 of each LED unit103 to expose opposite end portions of a bottom surface of the secondn-type GaN layer 40. Then the alkaline solution is used to etch androughen the exposed opposite end portions of the bottom surface of thesecond n-type GaN layer 40 of each LED unit 103. In order to acceleratethe etching speed, the alkaline solution can be strong alkalinesolution, such as KOH solution, NaOH solution etc. For example, theconnecting layer 30 and the second n-type GaN layer 40 can be etched byKOH solution with a temperature of 85 degree centigrade for 30 to 60minutes.

Referring to FIG. 9, the sixth step is to separate the LED units 103along the cutting channels 102 to obtain a number of LEDs 100.

It is understood, in other embodiments, the LED 100 would not includethe transparent conductive layer 70; thus, the p-type electrode 80 canbe directly formed on the p-type GaN layer 60. Furthermore, the fourthstep can also be arranged after the fifth step.

Referring to FIG. 10, a second method for manufacturing the LED 100according to the exemplary embodiment is shown. The second method issimilar to the first method; however only one LED 100 is obtained. Thesecond method includes following steps: providing the substrate 10;forming the first n-type GaN layer 20, the connecting layer 30, thesecond n-type GaN layer 40, the light emitting layer 50, the p-type GaNlayer 60, and the transparent conductive layer 70 on the substrate 10 insequence; etching the transparent conductive layer 70, the p-type GaNlayer 60, and the light emitting layer 50 to expose a portion of thesecond n-type GaN layer 40; forming the p-type electrode 80 on thetransparent conductive layer 70 and the n-type electrode 90 on theexposed portion of the second n-type GaN layer 40; and using alkalinesolution to etch away two opposite lateral ends of the connecting layer30 thereby exposing two opposite end portions of a bottom surface of thesecond n-type GaN layer 40; and etching and roughing the exposed twoopposite end portions of the bottom surface of the second n-type GaNlayer 40 by using the alkaline solution.

While certain embodiments have been described and exemplified above,various other embodiments will be apparent to those skilled in the artfrom the foregoing disclosure. The disclosure is not limited to theparticular embodiments described and exemplified, and the embodimentsare capable of considerable variation and modification without departurefrom the scope and spirit of the appended claims.

What is claimed is:
 1. An LED (light emitting diode) comprising: asubstrate; a first n-type GaN layer, a connecting layer, and a secondn-type GaN layer formed on the substrate in sequence, the connectinglayer being etchable by alkaline solution, a bottom surface of thesecond n-type GaN layer facing towards the connecting layer having aroughed exposed portion, a GaN on the bottom surface of the secondn-type GaN layer being an N-face GaN, a top surface of the second n-typeGaN layer facing away from the connecting layer comprising a first areaand a second area; and a light emitting layer, and a p-type GaN layerformed on the first area of the top surface of the second n-type GaNlayer in sequence.
 2. The LED as claimed in claim 1, wherein a p-typeelectrode is formed on the p-type GaN layer, and an n-type electrode isformed on the second area of the second n-type GaN layer.
 3. The LED asclaimed in claim 2, wherein the p-type electrode comprises a roundelectrically connecting portion and a linear electrically spreadingportion, the electrically connecting portion and the n-type electrodeare located at two opposite ends of the LED respectively, theelectrically spreading portion extends from the electrically connectingportion towards the n-type electrode.
 4. The LED as claimed in claim 2,wherein a transparent conductive layer is disposed between the p-typeelectrode and the p-type GaN layer.
 5. The LED as claimed in claim 1,wherein the first n-type GaN layer has a first surface facing away fromthe substrate, and a GaN on the first surface of the first n-type GaNlayer is a Ga-face GaN.
 6. The LED as claimed in claim 1, wherein theconnecting layer is made of a material selected from a group consistingof AlN, SiO₂, and silicon nitride.
 7. The LED as claimed in claim 1,wherein a thickness of the connecting layer is in a range from 5nm to1000nm.